Device and method for scanning a document

ABSTRACT

A device for scanning a document is provided. A document placed on a support surface is scanned line by line by a camera that is provided with an optoelectronic line sensor, and electric signals are produced. The line sensor includes a plurality of image recording elements disposed in a linear orientation. A lens system is used to image the light reflected by the document to be captured onto a part of the image recording elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a camera provided with aphotoelectronic line sensor scans a document lying on a support surfaceline-by-line and generates electrical signals. The line sensor comprisesa plurality of image detection elements arranged in a line.

2. Description of the Related Art

In known devices to scan a document, light-sensitive cells are linearlyarranged in a line in order to determine (with the aid of an electricalsignal) the intensity of the light impinging on these light-sensitivecells. Such light-sensitive cells can, for example, be CCD sensors(charge coupled device) that are fashioned as one- or two-dimensionalCCD sensor arrangements. At least the line of the document to be scannedis illuminated with the aid of a light source. The light reflected bythe document is supplied to the image detection elements of the CCD linesensor. The image detection elements generate an electrical chargecorresponding to the supplied light.

After the detection of one line, the charge quantity of each imageelement is determined, in that the stored charge is, for example,supplied to an analog-digital converter. Either the document and/or thescanning device is subsequently shifted such that the next line can bescanned. Such devices for scanning a document are also designated asscanners that can, for example, be executed as flatbed scanners, handscanners or drum scanners. In such known scanning devices, a document isilluminated in lines, whereby a camera records graphical elements of thedocument line-by-line and subsequently generates image data that aresubsequently further processed. The width of the support surface and thenumber of the linearly arranged image detection elements define theresolution with which the image elements of the line of the document tobe scanned are recorded.

Depending on the document to be recorded, different requirements areplaced on the resolution with which the document should be recorded. Itis thus frequently necessary that photos must be recorded with anoptimally high resolution, however text can be recorded with a lowerresolution. Thus in the prior art it is known to scan only every secondpossible line of the document. The scanning speed of the document canthereby be nearly doubled. Depending on the application field, therequirements for the image quality and the scanning speed can vary quitesignificantly. Thus in general a high scanning capacity at lower imagequality, i.e. at lower resolution, is opposite to a lower scanning speedwith higher image quality. Known devices to scan a document can react tothese different requirements only in a limited manner. An adaptation tothe different requirements can, for example, ensue via the exchange ofthe optoelectric line sensor and the associated optics. However, thisexchange is connected with a large technical and financial expenditure.

An image reader in which an image to be recorded is recorded with theaid of a CCD image sensor is known from German Patent Document DE 30 39139 A1. The light reflected by the document is deflected to the imagesensor with the aid of a mirror. The deflected light is focused on theimage sensor with the aid of an objective.

From German Patent Document DE 41 43 483 C2, a document reader is knownthat scans a document over a predetermined scan width along a primaryscanning direction with the aid of a light beam. The light reflected bythe document is detected with a photoconductive device. The reflectedlight is imaged with the aid of an objective on the photoconductivedevice.

From the Japanese Patent Document JP 7-30729 A it is known to image thelight reflected by a document on two sensor elements with the aid of alens and multiple reflection elements. The sensor elements respectivelyhave a different pixel count per length unit with which they detect thelight reflected by the document.

From the Japanese Patent Document JP 7-135556, it is known that thesignals of multiple sensor elements of a sensor line are averaged torecord the light reflected by a document corresponding to a targetresolution that is less than the physical resolution of the sensorelement.

From the Japanese Patent Document JP 5-68140 A, a line sensor is alsoknown that can be read out twice as fast with halved resolution. Amechanical movement of the optics that image the light reflected by thedocument onto the sensor element is not necessary.

From the Japanese Patent Document JP 2000-354158 A, an adjustable opticis known via which documents with different width or with differentresolution should be scanned, imaging the light reflected by thedocument onto the line sensor in a suitable manner. The respective widthof the document is then imaged onto the available width of the sensorwith the aid of the adjustable optic.

Further image generation devices are known from the documents U.S. Pat.No. 6,219,463 B1, European Patent Document EP 1 126 692 A and U.S. Pat.No. 6,215,563.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a simple device and a simplemethod to scan a document in which, given a reduction of the resolutionwith which the document is scanned, a corresponding increase of thescanning speed is simply achieved.

According to the invention, a device to scan a document includes acamera provided with an optoelectronic line sensor, the camera scanninga document lying on a support surface line for line and generatingelectrical signals, whereby the line sensor comprises a plurality oflinearly arranged image detection elements, and a lens arrangement that,in a first position, images light reflected by the line of the documentto be recorded onto essentially all image detection elements of the linesensor, and that in at least one second position the lens arrangementimages the light reflected by a document line onto a portion of theimage detection elements of the line sensor.

For better understanding of the present invention, in the followingreference is made to the preferred exemplary embodiment shown in thedrawings, which is described using specific terminology. However, it isto be noted that the protective scope of the invention should notthereby be limited, since such variations and modifications to the showndevice and the specified method as well as such further applications ofthe invention as it is shown therein are viewed as typical present orfuture expertise of a competent average man skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a scanning device to scan adocument; and

FIG. 2 is a schematic representation of a scanning device according toFIG. 1, whereby a region of an image detection element is covered withthe aid of a diaphragm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the inventive device, a lens arrangement is provided that images thelight reflected by the line of the document to be recorded onto aportion of the image detection elements. This is in particularadvantageous when the document should be recorded with a lowerresolution than the maximum resolution possible with this device. Theline of the document to be recorded can thereby be scanned by the linesensor with a correspondingly higher speed than given recording of theline at a higher resolution.

The lens arrangement images the same line on only one portion of theimage detection elements of the line sensor, whereby only the electricalsignals generated by this portion of the image detection elements areread out from the line sensor and further processed. In particular givena linear readout of the electrical signals of the line sensor, only theelectrical signals of the image detection elements arranged in a row onwhich the lines of the document have been imaged must then be read out.In contrast to the prior art, the electrical signals of all imagedetection elements (of which only a part is subsequently furtherprocessed) thus no longer have to be read out; rather, only theelectrical signals of the image detection elements on which the line ofthe document has been imaged are read out.

Due to the imaging of the line of the document on only one portion ofthe image detection elements, the scanning of the line of the documentensues with a reduced resolution. Via this device to scan a document, itis possible that, given scanning of the document, the number of therecorded image elements is (even at a lower resolution) approximatelyequal to the number of the recorded image elements given recording of adocument with a high resolution. The scanning speed of the device canthereby be increased with little effort.

According to a second aspect, the invention concerns a method to scan adocument. With the aid of a lens arrangement, the light reflected by theline of the document to be recorded is imaged onto a portion of theimage detection elements. Only the electrical signals of the imagedetection elements on which the reflected light is imaged are furtherprocessed. It is thereby achieved that a document is scanned at a higherspeed at a reduced resolution.

With reference to the drawings, a scanning device 10 to scan a document12 is schematically shown in FIG. 1. In the device 10 shown in FIG. 1, adocument 12 to be scanned is arranged opposite a line sensor 14 withimage detection elements. The line sensor 14 comprises CCD imagedetection elements (charge coupled device) that are linearly arranged ina line. The document 12 is scanned line-by-line by the line sensor 14,in that the document 12 and/or the line sensor 14 are displacedline-by-line opposite to one another. The line of the document 12 to berecorded is illuminated with the aid of a light source (not shown),whereby the light reflected by the document 12 is imaged onto the imagedetection elements of the line sensor 14 via an optical system, forexample via a lens 16. The beam path for the imaging of the linereflected by the document 12 onto the line sensor 14 is indicated by therays 18, 20, and 22, whereby the ray 20 forms the optical axis of thelens 16. The image detection elements of the line sensor 14 are arrangedin a number and at a separation such that the lines of the document 12imaged on the line sensor 14 are recorded with a resolution of 400pixels per inch (dpi), i.e. with 400 pixels per 2.54 cm. Other scanningresolutions are of course possible. The line sensor 14 and the lens 16form a camera 38 for line-by-line scanning of the document 12.

Should the document 12 be recorded with only a resolution of 200 dpiinstead of 400 dpi, for example to reduce the amount of data, in knowndevices 10 to scan a document 12 the line of the document 12 to berecorded is imaged onto the line sensor 14 with the aid of the lens 16,and the signals of the line sensor 14 generated from the image detectionelements are read out, whereby only the electrical signals of everysecond image detection element are further processed. Given relativelycost-effective CCD sensors, it is necessary that the electrical signalsof the image detection elements are read out in series, since a directaddressing of individual image detection elements (i.e. the specificreadout of individual image detection elements) is not possible. Thus,even given a reduction of the resolution, no faster scanning of a lineis possible to record the electrical signals of the line to be scanned.An accelerated recording of the document 12 to be scanned in knownscanners 10 only results in that (for example given a halving of theresolution) only every second line of the document 12 has to berecorded.

In the inventive scanning device 10, should the line of the document 12be recorded with a lower resolution, the lens 16 is exchanged with alens 24 that images the light reflected by the document 12 onto only oneregion 26 of the line sensor 14, i.e. only onto one portion of the imagedetection elements of the line sensor 14. Given a reduction of theresolution from 400 dpi to 200 dpi, the lens 24 images the lightreflected by the line of the document 12 to be recorded onto the region26 of the line sensor 14, which essentially comprises half of the imagedetection elements that are used to record the same line of the document12 with a resolution of 400 dpi. The electrical signals of the imagedetection elements of the region 26 are read out in series from the linesensor 14 for further processing, whereby the electrical signals of theimage detection elements that are contained in the region designatedwith the reference character 28 are not read out.

Even given CCD sensors to be read out linearly, it is simply possible toread out electrical signals of image detection elements arranged next toone another of a region 26 of the CCD line sensor 14. Upon scanning ofthe line of the document 12, the image detection elements of the region28 of the line sensor 14 are not read out or, respectively, are nolonger read out. The beam path to image the line of the document 12 tobe scanned onto the region 26 of the line sensor 14 via the lens 24 isclarified by the rays 30, 32, and 34 shown with dashed lines, wherebythe ray 34 forms the optical axis of the lens 24. Given a reduction ofthe resolution from 400 dpi to 200 dpi, i.e. given a halving of theresolution, the optical axis 32 of the lens 24 is shifted byapproximately ¼ of the width of the line sensor 14 to the optical axis20 of the lens 16, in order to image the line of the document 12 to berecorded on the right region 26 of the line sensor 14. The region 26 ofthe line sensor 14 begins at the outer edge of the line sensor 14,whereby the electrical signals of the image detection elements of theregion 26 can be simple recorded via readout of the first right half ofthe image detection elements of the line sensor 14.

The scanning device 10 according to FIG. 1 is shown in FIG. 2, wherebythe image elements of the region 28 of the line sensor 14 are coveredwith the aid of a diaphragm 36, such that no light can impinge on theimage elements of the region 28. If the line of the document 12 to berecorded is imaged onto the region 26 of the line sensor 14 with the aidof the lens 24, via the diaphragm 36 it is achieved that no light, inparticular no scatter light, is detected by the image elements of theregion 28. Upon readout of the electrical signals of the image elementsof the line sensor 14, given relatively cost-effective CCD line sensors14 only the electrical signal of the first image element, of the linesensor 14 is always read out. After the readout of the electricalsignal, the charges of the image detection elements following to theleft are shifted to the right like a type of shift register, such thatvia the light impinging on the image detection elements, the electricalcharge generated in the respective image detection element is shifted insuccession into the storage of the image element arranged farthest tothe right and is read out from the right most image element. Via theshifting of the charge, image elements without charge are generatedbeginning with the outermost left image element.

The diaphragm 36 prevents the generation of an electrical charge (forexample via scatter light) by the image element of the region 28 of theline sensor 14 upon recording of the line of the document 12 to bescanned. No charges which could falsify subsequent measurement resultsare thereby subsequently shifted into the storage of the image detectionelements of the region 26 upon readout of the electrical signals of theimage detection elements of the region 28. After the readout of theelectrical signals of the image detection elements of the region 26, thecharges stored in the image detection elements of the region 28 havebeen shifted into the image detection elements of the region 26.However, no electrical charges are generated by the image detectionelements of the region 28. The image detection elements of the region 26are thus already charge-free after the readout of the image elements ofthe region 26, since no electrical charges that could be shifted fromthe region 28 into the region 26 are generated due to the diaphragm 36in the region 38.

It is not mandatory, for example, to provide the diaphragm 36 inembodiments in which the charge of the image elements of the CCD linesensor 14 is removed in another manner and/or the charges of the imageelements of the region 28 are not shifted into the image elements of theregion 26. In the exemplary embodiment according to FIGS. 1 and 2,depending on the desired resolution either the lens 16 or the lens 24 isarranged between the document 12 and the line sensor. In otherembodiments of the invention, however, the position of the lens 16 orthe lens 24 can also be changed such that only one part of the line ofthe document 12 to be recorded is imaged on the region 26 of the linesensor 14 with the aid of the lens 16.

Instead of the lens 16, 24, however, in further embodiments it is alsopossible to provide a zoom lens system whose optical axes 20, 32 can bedisplaced relative to the line sensor 14. However, it is also possibleto displace the position of the line sensor 14 such that the line of thedocument 12 to be scanned is imaged in a first position onto the region26 of the line sensor 14, whereby a resolution of 200 dpi results, andin a second position the line is imaged onto the regions 28 and 26 ofthe line sensor 14, whereby the line is recorded with a resolution of400 dpi. The electrical charge signals recorded and read out from theline sensor 14 can subsequently be supplied to an analog-digitalconverter that converts the electrical charge signals of the imagedetection elements into digital signals.

If the scanning device 10 according to FIG. 1 or 2 has a line sensor 14that records a document line of 300 mm width with 400 dpi, i.e. in thatapproximately 5000 image detection elements are arranged linearly nextto one another to record the document line, approximately 4000 lines arescanned per second by the device 10 when the line sensor 14 has aprocessing speed of 20 million pixel signals per second. At a resolutionof 400 dpi, a scanning speed of 25.4 mm per second results.

Should the same document 12 be scanned with only a resolution of 200dpi, only every second line of the document 12 is scanned. Theresolution of 200 dpi between the lines, which is also designated as atransport resolution, is achieved via a corresponding advance of theline sensor 14 and/or the document 12. The scanning speed given 4000recorded lines per second can thereby be doubled to approximately 50.8mm per second.

If the light reflected by the line of the document 12 to be recorded isalso mapped to only the half (i.e. the region 26) of the line sensor 14,as already specified in connection with FIGS. 1 and 2, the imageelements of the line can thereby also be recorded with a resolution ofonly 200 dpi, whereby a line with 300 mm document width is recorded with2500 image detection elements and 8000 lines of the document 12 arescanned by the device 10 per second. The processing speed is therebyincreased to 101.6 mm per second.

If a document 12 to be scanned with a resolution of 200 dpi has, forexample, only a width of 210 mm, only 1750 image elements or,respectively, pixels are necessary to scan one line. Given a processingspeed of the line sensor 14 of 20 million pixels per second, thus 11428lines can be scanned per second, whereby a scan speed of 145.1 mm persecond is achieved at a scanning resolution of 200 dpi.

Although a preferred exemplary embodiment is displayed and described indetail in the drawings and in the preceding specification, this shouldbe viewed as purely exemplary and not as limiting the invention. It isto be noted that only the preferred exemplary embodiment is shown anddescribed, and all variations and modifications that presently and inthe future line within the protective scope of the invention should beprotected.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

1-3. (canceled)
 4. A device to scan a document, comprising: a supportsurface for supporting a document to be scanned; a camera having anoptoelectronic line sensor, said line sensor being disposed to performline by line scanning of the document on said support surface, said linesensor generating electrical signals by said scanning of the document,said line sensor including a plurality of linearly arranged imagedetection elements; a lens arrangement having a first position and asecond position, said lens arrangement in said first position imaginglight reflected by a line of the document to be recorded onsubstantially all of said plurality of image detection elements of saidline sensor, said lens arrangement in at least said second positionimaging light reflected by a document line onto a portion of said imagedetection elements of said line sensor.
 5. A device according to claim1, wherein said lens arrangement has different optical axes in saidfirst and second positions.
 6. A device according to claim 1, wherein insaid first position said lens arrangement includes a first lens elementand in said second position said lens arrangement includes a second lenselement, said first and second lens elements being exchanged with oneanother given a position change; electrical signals of said imagedetection elements onto which the reflected light is imaged beingfurther processed; in said first position said lens arrangement imagesthe light reflected by a document line onto essentially all of saidimage detection elements of said line sensor; and in said at least onesecond position the light reflected by a document line is imaged onto aportion of said image detection elements of said line sensor.
 7. Anoptical scanning device for scanning a document, comprising: a documentstation support constructed and configured to support a document to bescanned; an arrangement of image sensor elements disposed to detectlight reflected from the document and operable to generate electricalsignals corresponding to the light from the document; and a lens systemhaving a first position and a second position, said lens system beingoperable to focus light reflected from the document onto a first portionof said arrangement of image sensor elements when said lens system is insaid first position, said lens system being operable to focus lightreflected from the document onto only a second portion of saidarrangement of image sensor elements when said lens system is in saidsecond position, said second portion of said image sensor elements forsaid second position of said lens being substantially less than saidfirst portion of said image sensor elements for said first position ofsaid lens.
 8. An optical scanning device as claimed in claim 7, whereinsaid arrangement of image sensor elements is a linear arrangement ofsensor elements.
 9. An optical scanning device as claimed in claim 7,wherein said arrangement of image sensor elements is an arrangement ofCCD sensor elements.
 10. An optical scanning device as claimed in claim7, wherein said arrangement of image sensor elements is a lineararrangement of sensor elements.
 11. An optical scanning device asclaimed in claim 7, wherein said lens system has a first optical axis insaid first position and a second optical axis in said second position.12. An optical scanning device as claimed in claim 7, wherein said lenssystem include a first set of lenses in said first position and a secondset of lenses in said second position.
 13. An optical scanning device asclaimed in claim 7, wherein said image sensor elements of said firstportion includes all of said image sensor elements of said secondportion and includes image sensor elements that receive no lightreflected from the document when said lens system is in said secondposition.
 14. An optical scanning device as claimed in claim 7, whereinsaid lens system is movable between said first position and said secondposition.
 15. An optical scanning device as claimed in claim 14, whereinsaid arrangement of image sensor elements is of a predetermined length,and said lens system is moved between said first position and saidsecond position by a distance of approximately one fourth of saidpredetermined length.
 16. An optical scanning device as claimed in claim7, further comprising: a diaphragm operable to cover ones of said imagesensor elements, said diaphragm leaving said second portion of saidimage sensor elements exposed when said lens system is in said secondposition.
 17. An optical scanning device as claimed in claim 16, whereinsaid first position and said second position of said lens system are asame physical position of elements of said lens system.
 18. An opticalscanning device as claimed in claim 7, wherein said first position andsaid second position corresponds to first and second positions of saidarrangement of image sensor elements, said arrangement of image sensorelements being selectively movable between said first and secondpositions.
 19. An optical scanning device for scanning a document,comprising: a document station support constructed and configured tosupport a document to be scanned; an arrangement of image sensorelements disposed in a linear array to detect light reflected from thedocument and operable to generate electrical signals corresponding tothe light from the document, said arrangement of image sensorsperforming line by line scanning of the document; and a lens system thatis movable between a first position and a second position, said lenssystem being operable to focus light reflected from substantially anentire line of the document during line by line scanning onto a firstportion of said arrangement of image sensor elements when said lenssystem is in said first position, said lens system being operable tofocus light reflected from substantially an entire line of the documentduring line by line scanning onto only a second portion of saidarrangement of image sensor elements when said lens system is in saidsecond position, said second portion of said image sensor elements forsaid second position of said lens being substantially less than saidfirst portion of said image sensor elements for said first position ofsaid lens.
 20. An optical scanning device as claimed in claim 19,wherein said lens system include a first set of lens corresponding tosaid first position and a second set of lenses corresponding to saidsecond position.